Manufacturing apparatus and method for carbon nanotube

ABSTRACT

A manufacturing apparatus, including: two electrodes whose forwardmost end portions are opposed to each other; a power supply which applies a voltage between the electrodes in order to generate discharge plasma in a discharge area between the electrodes; and plural magnets that form a magnetic field in the generation area of the discharge plasma by generating a magnetic field from a magnetic pole surface of each of the plural magnets that are arranged to have the magnetic pole surfaces thereof opposed to one imaginary axis within a space; and of the two electrodes, at least a part of one electrode is located in an area surrounded by: an imaginary plane formed by connecting end portions of the magnetic pole surfaces of the plural magnets on one side in a direction of the imaginary axis.

This application is a U.S. National Stage Application of InternationalApplication No. PCT/JP02/11305 filed Oct. 30, 2002.

TECHNICAL FIELD

The present invention relates to a manufacturing apparatus and methodfor a carbon nanotube whose industrial availability has been attractingattention in recent years.

BACKGROUND ART

The material having a diameter of 1 μm or smaller which is finer thancarbon fibers is generally called carbon nanotubes and distinguishedfrom the carbon fibers. However, there is no particularly definiteboundary therebetween. By a narrow definition, the material whose carbonfaces with hexagon meshes are substantially parallel to an axis iscalled a carbon nanotube, and even a variant of the carbon nanotube,around which amorphous carbon exists, is included in the carbon nanotube(Note that the narrow definition is applied to the carbon nanotubeaccording to the present invention.).

Usually, the narrowly-defined carbon nanotubes are further classifiedinto two types: carbon nanotubes having a structure with a singlehexagon mesh tube (graphene sheet) are called single wall nanotubes(hereinafter, simply referred to as “SWNT” in some cases); and on theother hand, the carbon nanotubes made of multilayer graphene sheets arecalled multi-wall nanotubes (hereinafter, simply referred to as “MWNT”in some cases). The carbon nanotubes of these types have an extremelyfiner diameter than that of the carbon fibers, a high Young's modulus,and high electrical conductivity, thereby attracting attention as a newindustrial material.

Thus, the carbon nanotube is a new material whose structural element isonly carbon, and is mechanically extremely strong enough to exceed aYoung's modulus of 1 TPa. In addition, electrons flowing through thecarbon nanotube easily undergo ballistic transport, so that it ispossible to flow a large quantity of current. Further, the carbonnanotube has a high aspect ratio, so that its application to a fieldelectron emitting source is underway, and a light emitting element anddisplay having a high brightness is under development. Furthermore, somesingle wall carbon nanotubes exhibit semiconductor characteristics, andare applied to the experimental manufacture of a diode and a transistor.Therefore, its application is especially desired in a field offunctional materials and in a field of an electronic industry.

Conventionally, it has been known that fullerenes and carbon nanotubescan be manufactured by methods including resistance heating, plasmadischarge such as arc discharge with a carbon rod as a raw material,laser ablation, and chemical vapor deposition (CVD) using acetylene gas.However, a mechanism of generating carbon nanotubes with those methodsis controversial in various respects, and a detailed growth mechanism isnot disclosed even now.

With regard to the manufacture of a carbon nanotube, various methods andimprovements have been studied for the purpose of synthesis in a largequantity. The resistance heating which was devised in the early stage isa method of heating and vaporizing graphite by bringing the forward endsof two pieces of graphite in contact with each other in a rare gas, andthen applying a current of several tens to several hundreds of amperes.However, with this method, it is extremely difficult to obtain a fewgrams of specimen, so that the method is hardly used now.

The arc discharge is a method of synthesizing fullerenes and carbonnanotubes by generating arc discharge in a rare gas such as He and Arwhile using graphite rods as an anode and a cathode. The forward endportion of the anode reaches a high temperature of 4000° C. or more byarc plasma generated by the arc discharge, then the forward end portionof the anode is vaporized, and a large quantity of carbon radicals andneutral particles are generated. The carbon radicals and neutralparticles repeat collision in the plasma, further generate carbonradicals and ions, and become soot containing fullerenes and carbonnanotubes to be deposited around the anode and cathodes and on the innerwall of an apparatus. When the anode includes an Ni compound, a ferrouscompound, or a rare earth compound, which acts as catalyst, single wallcarbon nanotubes are synthesized efficiently.

The laser ablation is a method of irradiating a pulse YAG laser beam ona graphite target, generating high density plasma on the surface of thegraphite target, and generating fullerenes and carbon nanotubes. Thecharacteristic of the method is that a carbon nanotube having arelatively high purity can be obtained even at a growth temperature ofmore than 1000° C.

A technique for higher purity synthesis of the SWNT for the purpose ofincreasing the purity in the laser ablation is reported in A. Thess et.al, “Nature”, Vol. 273, p. 483-487. However, the laser ablation suppliesonly a small quantity of carbon nanotubes, and the efficiency is low,leading to higher costs of carbon nanotubes. In addition, the purityremains about 70 to 90%, and is not sufficiently high.

The chemical vapor deposition is a method of generating carbon nanotubesby a chemical decomposition reaction of the raw material gas, using anacetylene gas, a methane gas, or the like containing carbon as a rawmaterial. The chemical vapor deposition depends on a chemical reactionoccurring in a thermal decomposition process of the methane gas and thelike serving as the raw material, thereby enabling the manufacture of acarbon nanotube having a high purity.

However, in the chemical vapor deposition, the growth rate of the carbonnanotube is extremely low, so that the efficiency is low and theindustrial application is difficult. In addition, the structure of themanufactured carbon nanotube has more defects and is incomplete comparedwith that synthesized in the arc discharge or the laser ablation.

The use of a vertical furnace enables continuous growth, therebyrealizing a growth apparatus having a high production capability.However, in that case, the purity of the obtained carbon nanotuberemains low.

Electrons, ions of carbon, radicals, and neutral particles in the arcplasma generated by the arc discharge repeat recollision, therebygenerating complex chemical reactions, so that it is difficult to stablycontrol the density and the kinetic energy of the carbon ions. Thus, alarge quantity of amorphous carbon particles and graphite particles aregenerated simultaneously along with the fullerenes and the carbonnanotubes, all of which exist in a mixed state as soot.

Therefore, when the fullerenes and the carbon nanotubes are to be usedfor the industrial application, it is necessary to purify and separateonly the fullerenes and the carbon nanotubes from the soot. Inparticular, the carbon nanotubes does not dissolve in a solvent, so thatthe purification thereof is conducted by combining centrifugation,oxidation, filtering, and the like. However, physical properties andchemical properties of the carbon nanotubes, and those of the amorphouscarbon particles and the graphite particles, which are major impurity,are approximately the same, thereby making it difficult to remove theimpurity completely. Thus, high purity carbon nanotubes are obtained byrepeating purification. It is also known that, in the purificationprocess, alkali metal may remain due to the influence of a surfaceactive agent used as a dispersing agent, and the influence of themechanical damage is extensive as well in the purification process,thereby causing a large quantity of defects in the carbon nanotubes.

To solve this problem, in the synthesis stage of the carbon nanotubes, asynthesis technique is desired for high purity carbon nanotubesincluding as less impurities as possible, that is, such carbon nanotubesas to include no amorphous carbon particles nor graphite particles.

Therefore, an object of the present invention is to solve the problemsof the above-mentioned conventional art. Specifically, the presentinvention has an object to provide a manufacturing apparatus and methodwhich can efficiently synthesize a high purity carbon nanotube having anextremely low concentration of impurities such as the amorphous carbonand graphite particles on an industrial basis.

DISCLOSURE OF THE INVENTION

Generally, when discharge plasma is generated in a magnetic field, dueto an interaction between the discharge plasma and the magnetic field,charged particles are confined in the magnetic field, thereby increasingan average free path length of the charged particles. Therefore, theprobability increases that the charged particles collides with eachother or with neutral particles coexisting in the plasma, therebyimproving the reaction efficiency.

The present inventors found that by applying this phenomenon to themanufacture of a carbon nanotube, a high purity carbon nanotube can beefficiently provided on an industrial basis, which have an extremely lowconcentration of impurities such as the amorphous carbon particles andthe graphite particles, which leads to the present invention. That is,the present invention provides a manufacturing apparatus for a carbonnanotube, including at least: two electrodes whose forwardmost endportions are opposed to each other; a power supply which applies avoltage between the electrodes in order to generate discharge plasma ina discharge area between the electrodes; and plural magnets that form amagnetic field in the generation area of the discharge plasma bygenerating a magnetic field from a magnetic pole surface of each of theplural magnets, characterized in that:

the plural magnets are arranged to have the magnetic pole surfacesthereof opposed to one imaginary axis within a space; and

of the two electrodes, at least a part of one electrode is located in anarea surrounded by: an imaginary plane formed by connecting end portionsof the magnetic pole surfaces of the plural magnets on one side in adirection of the imaginary axis; an imaginary plane formed by connectingend portions thereof on the other side; and the magnetic pole surfacesof the plural magnets, and the forwardmost end portion of the otherelectrode is located in an area outside the area between the twoimaginary planes.

According to the manufacturing apparatus for a carbon nanotube accordingto the present invention, it is possible to efficiently synthesize ahigh purity carbon nanotube on an industrial basis. It is assumed thatthis is because the discharge plasma including radicals such as C⁺, C,and C₂, can be confined in a predetermined magnetic field by generatingthe discharge plasma in the magnetic field, so that the collisionprobability of the charged particles in the discharge plasma isincreased, thereby making it possible to increase the efficiency ofgenerating the carbon nanotube. Also, it is assumed that by locating thetwo electrodes in such a predetermined position as described above withrespect to the magnets, the magnetic flux density of the magnetic fieldhaving the vector component appropriate for confining the dischargeplasma is greatly increased, thereby further increasing the purity of acarbon nanotube to be manufactured.

At this time, the one electrode is preferably an anode. By arranging theone electrode as the anode, the other electrode to be a cathode islocated in the area outside the area between the imaginary plane formedby connecting the end portions of the magnetic pole surfaces of theplural magnets on one side in the direction of the imaginary axis andthe imaginary plane formed by connecting the end portions thereof on theother side. Carbon nanotubes grow and are deposited on the cathode, sothat the manufactured carbon nanotubes are located in the positionoutside the area sandwiched between or surrounded by the magnetic polesurfaces of the plural magnets. Therefore, in collecting themanufactured carbon nanotubes or replacing the electrodes, it isunnecessary to take out the other electrode from the area sandwichedbetween or surrounded by the magnetic pole surfaces of the pluralmagnets. That is, the manufactured carbon nanotubes can be collectedwithout moving the other electrode, and the electrodes can be replacedby sliding the electrode in a direction perpendicular to the takeoutoperation. Accordingly, if the carbon nanotubes are located in theposition outside the area sandwiched between or surrounded by themagnetic pole surfaces of the plural magnets, it becomes easy to handlethe carbon nanotubes, thereby realizing the increase in highproductivity for the carbon nanotubes.

In order to replace the electrodes sequentially, there can be given aform in which plural rod-shaped electrodes are provided, the pluralrod-shaped electrodes are placed in parallel in a bristling manner, andany one of the rod-shaped electrodes has a forwardmost end portionopposed to the forwardmost end portion of the one electrode and can bemoved to a position so as to serve as the other electrode.

Further, it is preferable to provide collecting means for collecting thecarbon nanotubes that are manufactured by generating the dischargeplasma between the two electrodes and remain adhering to the forwardmostend portion of the other electrode. Examples of the collecting meansinclude the one having a mechanism for scraping off the carbon nanotubesadhering to the forwardmost end portion of the other electrode, and theone having a mechanism for drawing the carbon nanotubes adhering to theforwardmost end portion of the other electrode.

According to the manufacturing apparatus for a carbon nanotube of thepresent invention, the discharge plasma generated in the discharge areais preferably arc plasma.

According to the manufacturing apparatus for a carbon nanotube of thepresent invention, arrangements of the plural magnets include a form inwhich the plural magnets are arranged to surround the one electrode suchthat all the magnetic pole surfaces of the same poles are opposed to theimaginary axis, and a form in which the even number of magnets, equal toor greater than four, are arranged to surround the one electrode suchthat each magnetic pole surface opposed to the imaginary axis has a polealternately opposite to that of the adjacent magnetic pole surface.

According to the manufacturing apparatus for a carbon nanotube of thepresent invention, of the two electrodes, a magnetic flux density at anedge of the forwardmost end portion of the electrode that generates thedischarge plasma is preferably 10⁻⁵ T or more and 1 T or less, and adensity of a discharge current at a time of generating the dischargeplasma is preferably 0.05 A/mm² or more and 15 A/mm² or less withrespect to an area of the forwardmost end portion of the electrode thatgenerates the discharge plasma. Also, the voltage applied to theelectrodes by the power supply is preferably 1 V or more and 30 V orless.

According to the manufacturing apparatus for a carbon nanotube of thepresent invention, an area of the forwardmost end portion of a cathodeof the two electrodes is preferably equal to or less than the area ofthe forwardmost end portion of the anode thereof.

According to the manufacturing apparatus for a carbon nanotube of thepresent invention, at least the discharge area and the two electrodescan be received in a sealed container. In this case, atmosphereadjusting means capable of adjusting an atmosphere inside a sealedcontainer is preferably provided.

According to the manufacturing apparatus for a carbon nanotube of thepresent invention, the material of the electrodes is preferably carbonor a substance that contains carbon and has an electric resistivityequal to or more than 0.01 Ω·cm and equal to or less than 10 Ω·cm.

On the other hand, a manufacturing method for a carbon nanotubeaccording to the present invention is characterized in that: theabove-mentioned manufacturing apparatus for a carbon nanotube of thepresent invention is used; and by applying a voltage between the twoelectrodes inside the manufacturing apparatus, discharge plasma isgenerated in a discharge area between the electrodes to therebymanufacture the carbon nanotube. At this time, a voltage applied betweenthe two electrodes is preferably a DC voltage such that the oneelectrode of the manufacturing apparatus for a carbon nanotube of thepresent invention is an anode. Also, the discharge plasma generated inthe discharge area is preferably arc plasma.

According to the manufacturing method for a carbon nanotube of thepresent invention, a pressure of an atmosphere of the discharge area ispreferably 0.01 Pa or more and 510 kPa or less, and an atmosphere of thedischarge area is preferably a gas atmosphere that contains at least oneof gases selected from air, helium, argon, xenon, neon, nitrogen, andhydrogen. Also, an atmosphere of the discharge area preferably furtherincludes a gas that is composed of a substance containing carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view showing a manufacturingapparatus for a carbon nanotube according to Embodiment Mode 1 of thepresent invention;

FIG. 2 is a cross sectional view (cross sectional view of only permanentmagnets and an electrode) taken along a line A-A of FIG. 1;

FIG. 3 is a plan view showing an example of an arrangement of magnets;

FIG. 4 is a plan view showing an example of the arrangement of magnets;

FIG. 5 is a plan view showing an example of the arrangement of magnets;

FIG. 6 is a plan view showing an example of the arrangement of magnets;

FIG. 7 is a plan view showing an example of the arrangement of magnets;

FIG. 8 is a plan view showing an example of the arrangement of magnets;

FIG. 9 is a plan view showing an example of the arrangement of magnets;

FIG. 10 is a plan view showing an example of the arrangement of magnets;

FIG. 11 is a plan view showing an example of the arrangement of magnetsand directions of magnetic poles;

FIG. 12 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 13 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 14 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 15 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 16 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 17 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 18 is a plan view showing an example of the arrangement of magnetsand the directions of magnetic poles;

FIG. 19 is a schematic view showing a state of lines of magnetic forcein the case where the permanent magnets are arranged such that all themagnetic pole surfaces of the same poles are opposed to an imaginaryaxis in the manufacturing apparatus of FIG. 1;

FIG. 20 is a schematic view showing a state of lines of magnetic forcein the case where the permanent magnets are arranged such that eachmagnetic pole surface opposed to the imaginary axis has the N or S polealternately opposite to that of the adjacent magnetic pole surface inthe manufacturing apparatus of FIG. 1;

FIG. 21 is a perspective view showing an example of an electromagnetapplicable to the present invention as a magnet;

FIG. 22 is a perspective view showing another example of theelectromagnet applicable to the present invention as a magnet;

FIG. 23 is a schematic cross sectional view showing an arrangement ofelectrodes in the manufacturing apparatus of FIG. 1;

FIG. 24 is a schematic cross sectional view showing an example of anarrangement of electrodes which can be adopted in the present invention;

FIG. 25 is a schematic cross sectional view showing another example ofthe arrangement of electrodes which can be adopted in the presentinvention;

FIG. 26 is a schematic cross sectional view showing further anotherexample of the arrangement of electrodes which can be adopted in thepresent invention;

FIG. 27-a is a schematic cross sectional view showing an example ofcooling means formed by attaching a heat releasing member to thepermanent magnet;

FIG. 27-b is a front view observed from the right (the side of a surfacewhich is opposed to the above-mentioned imaginary axis) of FIG. 27-a;

FIG. 28-a is a cross sectional view of the permanent magnets and aperiphery of the electrode taken along a direction of side surfacesthereof, which shows an example of the cooling means formed by attachingthe heat releasing member to each permanent magnet and furthersubjecting this to water cooling;

FIG. 28-b is a cross sectional view taken along a line B-B of FIG. 28-a;

FIG. 29 is a schematic cross sectional view showing a manufacturingapparatus for a carbon nanotube according to Embodiment Mode 2 of thepresent invention;

FIG. 30 is a cross sectional view (cross sectional view of onlypermanent magnets, electrodes, and a holding member) taken along a lineC-C of FIG. 29;

FIG. 31 is a schematic cross sectional view showing a manufacturingapparatus for a carbon nanotube according to Embodiment Mode 3 of thepresent invention;

FIG. 32 is an enlarged perspective view showing only a rotary member andcollecting means in a periphery there of which are extracted from FIG.31;

FIG. 33 is a graph showing a transition of a pertinent purity based on aposition of a forwardmost end portion of “the other electrode” (adistance h from a midpoint between an imaginary plane X and an imaginaryplane Y) in an example;

FIG. 34 is a scanning electron microscope photograph (at a magnifyingpower of 20000) of the forwardmost end portion of “the other electrode”when h=9 mm; and

FIG. 35 is a scanning electron microscope photograph (at a magnifyingpower of 20000) of the forwardmost end portion of “the other electrode”when h=15 mm.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail citingpreferred embodiment modes.

Embodiment Mode 1

FIG. 1 is a schematic cross sectional view showing a manufacturingapparatus for a carbon nanotube according to Embodiment Mode 1 of thepresent invention, and FIG. 2 is a schematic cross sectional view (crosssectional view of only permanent magnets and an electrode) taken along aline A-A of FIG. 1. The carbon nanotube manufacturing apparatusaccording to this embodiment mode shown in FIGS. 1 and 2 is structuredby arranging permanent magnets 20 to 23 in addition to a conventionalcarbon nanotube manufacturing apparatus using discharge plasma. Theconventional carbon nanotube manufacturing apparatus is composed of: twoelectrodes (an electrode 12 on one side serving as an anode, and anelectrode 11 on the other side serving as a cathode) having forwardmostend portions opposed to each other, which are disposed inside a reactioncontainer (chamber) 10 used as a sealed container; a moving apparatus 13that can slide the electrode 12 in a manner capable of adjusting theinterval between the electrode 11 and the electrode 12; a power supply18 for applying a voltage between the electrode 11 and the electrode 12;a vacuum pump 14 capable of decompressing the atmosphere in the reactioncontainer 10; a gas cylinder 17 for storing a desired gas; an inlet tube15 interconnecting between the gas cylinder 17 and the reactioncontainer 10; and atmosphere adjusting unit including a valve 19 capableof changing over the interconnection between opened and closed states.That is, a predetermined magnetic field is generated by the permanentmagnets 20 to 23 in a discharge area between the electrode 11 and theelectrode 12 in which the discharge plasma is generated when a voltageis applied between the electrode 11 and the electrode 12.

The permanent magnets 20 to 23 are arranged to surround the electrode12. Here, the permanent magnets 20 to 23 are arranged such that theirmagnetic pole surfaces (in the present invention, the term “magneticpole surface” refers to a magnet surface that has the S or N pole andgenerates a magnetic field) are opposed to the electrode 12.

Also, an area F is surrounded by: an imaginary plane X formed byconnecting end portions of the magnetic pole surfaces of the permanentmagnets 20 to 23 on one side in an axial direction of the electrode 12;an imaginary plane Y formed by connecting end portions thereof on theother side; and the magnetic pole surfaces of the permanent magnets 20to 23. The electrode 12 is located in the area F, and the forwardmostend portion of the electrode 11 is located in an area outside the areaF.

Thus, by generating the discharge plasma between the electrode 11 andthe electrode 12 in the predetermined magnetic field formed by thepermanent magnets 20 to 23, the discharge plasma including radicals suchas C⁺, C, and C₂ are confined in the magnetic field. Therefore, it isassumed that the collision probability of charged particles in thedischarge plasma is improved, thereby making it possible to increase theefficiency of generating the carbon nanotube. As a result, according tothis embodiment mode, it is possible to reduce inclusion of theamorphous carbon and graphite particles which result in the impurities.

Also, in this embodiment mode, a discharge area between the electrode 11and the electrode 12 is adjusted so as to be located in a positiondisplaced from a center position of the area surrounded by the permanentmagnets 20 to 23 (intermediate position between the imaginary plane Xand the imaginary plane Y along the axis of the electrode 12). At thecenter position of the area surrounded by the permanent magnets 20 to23, the direction of the formed magnetic field is, in most cases,orthogonal to the axial direction of the electrode 12, or the magneticfield is hardly formed since components of the magnetic field arecanceled out. When the generation area is displaced from the centerposition, the intensity of the magnetic field is increased, or themagnetic flux density of the magnetic field having the vector componenteffective for confining the discharge plasma is further increased.Therefore, it is assumed that the displacement of the center position asin this embodiment mode further increases the purity of the carbonnanotube to be manufactured.

Here, a description will be made of the arrangement of the respectivemagnets and respective electrodes of the present invention.

According to the present invention, the number of magnets is not limitedto four as in this embodiment mode, but may be two or more. However, asin this embodiment mode, such an arrangement as to surround the oneelectrode (electrode 12) is effective for confining the dischargeplasma, so that the number of magnets is preferably three or more.Naturally, even in the case of using two magnets, the magnets eachhaving an arc shape can be arranged to surround the one electrode, whichis a preferable form as well. There is no limit to the number ofmagnets.

According to the present invention, the plural magnets may be arrangedsuch that their respective magnetic pole surfaces are opposed to oneimaginary axis in a space. In this embodiment mode, the imaginary axiscoincides with the axis of the one electrode (that is, the magnetic polesurfaces of the permanent magnets 20 to 23 are opposed to the electrode12). However, the coincidence thereof is not always necessary.Naturally, the coincidence of the two axes is effective for confiningthe discharge plasma, so that the purity of the carbon nanotube to bemanufactured is further increased, which is preferable.

FIGS. 3 to 10 show examples of the arrangement of the magnets. In eachof the drawings, a black dot at the center indicates the imaginary axisdisposed perpendicularly to the paper with the drawing thereon, andareas hatched with oblique lines indicate the magnets. The magnets eachhave one magnetic pole surface opposed to the black dot and anothermagnetic pole surface as the back surface thereof.

FIGS. 3 and 4 show forms in which three magnets each having a planarshape are arranged to enclose a space. In this case, the imaginary axisis located in the position surrounded by the three magnets. In theexample shown in FIG. 3, the three magnets each have the same length andform an equilateral triangle (as an area formed by the magnetic polesurfaces). However, as in the example shown in FIG. 4, the three magnetsmay have different lengths or form a triangular shape other than theequilateral triangle.

FIGS. 5 and 6 show forms in which four magnets each having a planarshape are arranged to enclose a space. In this case, the imaginary axisis located in the position surrounded by the four magnets. In theexample shown in FIG. 5, the four magnets each have the same length andform a square (as an area formed by the magnetic pole surfaces).However, as in the example shown in FIG. 6, the four magnets may havedifferent lengths or form a quadrangular shape other than the square.

The number of magnets may be two or any number more than two. Naturally,the three or four magnets shown in FIGS. 3 to 6 may be changed into fivemagnets or more. FIG. 7 shows a form in which eight magnets each havinga planar shape are arranged to enclose a space. In this case, theimaginary axis is located in the position surrounded by the eightmagnets. In the example shown in FIG. 7, the eight magnets each have thesame length and form a regular polygon (as an area formed by themagnetic pole surfaces). However, the eight magnets may form a polygonwith five vertices or more other than the regular polygon. That is,naturally as in the form of FIG. 8, five magnets each having a planarshape may be arranged to enclose a space and form a pentagon having asomewhat flat shape.

FIGS. 9 and 10 show forms in which two magnets each having an arc shapeare arranged to opposed to each other. In this case, the imaginary axisis located in the position sandwiched between the arc-shaped magnetsopposed to each other. In the example shown in FIG. 9, the two magnetseach have the same arc length. However, as in the example shown in FIG.10, the two magnets may have different arc lengths.

Of the arrangements of the magnets exemplified above, the arrangementsare preferable in which the magnets surround the imaginary axis as inthe examples of FIGS. 3 to 10.

Some examples of the arrangements of the magnets have been givenhereinabove. However, according to the present invention, thearrangement of the magnets is not limited to the above examples.

The magnets are arranged such that one of the magnetic pole surfaces ofeach magnet is opposed to the imaginary axis. At this time, one of themagnetic pole surfaces having the S pole and the magnetic pole surfacehaving the N pole maybe opposed to the imaginary axis. FIGS. 13 to 18show examples of the directions of the magnetic pole surfaces. In eachof the drawings, a black dot at the center indicates the imaginary axisdisposed perpendicularly to the paper with the drawing thereon, areashatched with oblique lines indicate the S poles, and hollow areasindicate the N poles. The plane (or curved surface) on each side thereofindicates the magnetic pole surface of the corresponding pole.

FIGS. 11 and 12 show the examples of the directions of the magnetic polesurfaces in the arrangements of FIG. 3. In FIG. 11, all the threemagnets have the S poles directed toward the imaginary axis, while inFIG. 12, two S poles and one N pole are directed toward the imaginaryaxis. Alternatively, although not shown, all the three magnets may havethe N poles directed toward the imaginary axis. Further, although notshown, one S pole and two N poles may be directed toward the imaginaryaxis.

FIGS. 13 and 14 show the examples of the directions of the magnetic polesurfaces in the arrangements of FIG. 5. In FIG. 13, all the four magnetshave the S poles directed toward the imaginary axis, while in FIG. 14,two S poles and two N poles are directed toward the imaginary axis suchthat each magnetic pole surface opposed to the imaginary axis has a polealternately opposite to that of the adjacent magnetic pole surface.Alternatively, although not shown, all the four magnets may have the Npoles directed toward the imaginary axis.

FIGS. 15 and 16 show the examples of the directions of the magnetic polesurfaces in the arrangements of FIG. 7. In FIG. 15, all the eightmagnets have the S poles directed toward the imaginary axis, while inFIG. 16, four S poles and four N poles are directed toward the imaginaryaxis such that each magnetic pole surface opposed to the imaginary axishas a pole alternately opposite to that of the adjacent magnetic polesurface. Alternatively, although not shown, all the eight magnets mayhave the N poles directed toward the imaginary axis.

FIGS. 17 and 18 show the examples of the directions of the magnetic polesurfaces in the arrangements of FIG. 9. In FIG. 17, both the two magnetshave the S poles directed toward the imaginary axis, while in FIG. 18,one of the magnets has the S pole directed toward the imaginary axis andthe other has the N pole directed toward the imaginary axis.Alternatively, although not shown, both the two magnets may have the Npoles directed toward the imaginary axis.

Among the above examples of the directions of the magnetic pole surfacesgiven by FIGS. 13 to 18, one of the following two structures areeffective for confining the discharge plasma:

-   (A) a structure as exemplified in FIGS. 11, 13, 15, and 17, in which    the plural magnets are arranged to surround the imaginary axis (that    is, the one electrode) such that all the magnetic pole surfaces of    the same poles are opposed to the imaginary axis; and-   (B) a structure as exemplified in FIGS. 14 and 16, in which the even    number of magnets, equal to or greater than four, are arranged to    surround the one electrode such that each magnetic pole surface    opposed to the imaginary axis has a pole alternately opposite to    that of the adjacent magnetic pole surface. Accordingly, the purity    of the carbon nanotube to be manufactured is further increased,    which is preferable.

According to this embodiment mode shown in FIGS. 1 and 2, a descriptionwill be made of a state of the magnetic field in the case where themagnetic pole surfaces have the directions described in the aboverespective structures (A) and (B). FIG. 19 is a schematic view showing astate of lines of magnetic force in the above structure (A), that is, inthe case where the permanent magnets 20 to 23 are arranged such that allthe magnetic pole surfaces of the same poles are opposed to theimaginary axis. FIG. 20 is a schematic view showing a state of lines ofmagnetic force in the above structure (B), that is, in the case wherethe permanent magnets 20 to 23 are arranged such that each magnetic polesurface opposed to the imaginary axis has the N or S pole alternatelyopposite to that of the adjacent magnetic pole surface.

In the structure of FIG. 19, the lines of magnetic force emitted fromthe respective permanent magnets 20 to 23 toward the discharge area arerepulsive to each other, and an area indicated by F′ becomes a statesurrounded by the multi-directional lines of magnetic force.

In the structure of FIG. 20, the lines of magnetic force emitted fromthe respective permanent magnets 20 to 23 toward the discharge areaconverge on the adjacent permanent magnets, and an area indicated by F″becomes a state surrounded by the multi-directional lines of magneticforce.

As described above, according to the forms shown in FIGS. 19 and 20,multi-directional magnetic fields are acted on the area indicated by F′or F″. Thus, if the discharge plasma is generated in the area F′ or F″,it is assumed that the motion of the charged particles in the dischargeplasma is restricted in the space between the electrode 11 and theelectrode 12. If the carbon nanotube is thus manufactured, it ispossible to efficiently synthesize a high purity carbon nanotube havinga low impurity concentration at low costs on an industrial basis.

Note that in this embodiment mode, the permanent magnets 20 to 23 areused as the magnets. However, according to the present invention, themagnets are not limited to the permanent magnets, and may beelectromagnets that are each formed into a simple coil shape or formedby adding a magnetic core thereto. FIG. 21 is a perspective view showingan example of the electromagnet having a simple coil shape. FIG. 22 is aperspective view showing another example of the electromagnet formed byadding a magnetic core inside the coil.

In FIG. 21, reference numeral 24 denotes a cylindrical body formed of anon-magnetic substance, and an electromagnet is structured by winding acoil 26 around the cylindrical body 24. On the other hand, in FIG. 22, amagnetic core 28 is fitted and inserted to the inside of the cylindricalbody 24. From the viewpoint of increasing the magnetic flux density, theform shown in FIG. 22 with the magnetic core 28 fitted and inserted ispreferable, and may naturally be the form of FIG. 21.

In the electromagnet shown in FIG. 21, lines of magnetic forcepenetrates the electromagnet in the vertical direction in the drawing,so that disc-like surfaces formed by the coil 26 at both the left andright ends are magnetic pole surfaces, that is, surfaces that generatelines of magnetic force of the N pole and the S pole. The existence ofthe cylindrical body 24 does not affect the discussion on the magneticpole surfaces at all. If the left side in FIG. 21 is typified, a plane Pis the magnetic pole surface. Therefore, in the magnet in this case, themagnetic pole surface is not formed to be a physical surface, but isstructured by being formed imaginarily in a space.

On the other hand, in the electromagnet shown in FIG. 22, both the leftand right surfaces of the magnetic core 28 in the drawing are themagnetic pole surfaces, that is, the surfaces that generate lines ofmagnetic force of the N pole and the S pole. If the left side in FIG. 21is typified, a plane Q is the magnetic pole surface.

According to the present invention, the two electrodes are arranged onthe premise that the forwardmost ends thereof are opposed to each otherin order to generate discharge plasma, and that a magnetic field isgenerated in the generation area of the discharge plasma between boththe electrodes by a magnetic field generated from the magnetic polesurfaces of the plural magnets (in other words, that the generation areaof the discharge plasma between both the electrodes is in the positionon which the magnetic field due to the plural magnets effects). Further,the two electrodes are arranged on the essential condition that, of thetwo electrodes, at least a part of one electrode is located in an areasurrounded by: an imaginary plane formed by connecting end portions ofthe magnetic pole surfaces of the plural magnets on one side in adirection of the imaginary axis; an imaginary plane formed by connectingend portions thereof on the other side; and the magnetic pole surfacesof the plural magnets, and the forwardmost end portion of the otherelectrode is located in an area outside the area surrounded by the twoimaginary planes and the magnetic pole surfaces.

If FIG. 1 is used for explanation, according to the present invention,the imaginary axis coincides with the electrode 12, so that the twoimaginary planes correspond to the imaginary plane X formed byconnecting upper ends of the permanent magnets 20 to 23 in the axialdirection of the electrode 12 in the drawing, and the imaginary plane Yformed by similarly connecting lower ends thereof in the drawing. Thetwo electrodes 11 and 12 are arranged based on the area F surrounded bythose two imaginary planes X and Y and the permanent magnets 20 to 23 asa reference.

Note that regarding the “end portions in the imaginary axis direction”in the case of using the electromagnet as a magnet, the end portions ofthe electromagnet having no magnetic core as shown in FIG. 21 aredetermined based on the coil composing a main portion of theelectromagnet as a reference. If the example of FIG. 21 is used forexplanation and the vertical direction in the drawing is assumed to bethe imaginary axis direction, the positions indicated by the arrows Gand H are the “end portions in the imaginary axis direction”. Note thatin FIG. 21, the cylindrical body 24 and the coil 26 have no thicknessesfor the convenience of preparing the drawing. However, strictlyspeaking, those positions to be both end portions have no relationshipwith the cylindrical body 24, and fall on the center of the lead wire ofthe coil 26 (innermost lead wire thereof when wound around twice ormore).

On the other hand, the end portions of the electromagnet having amagnetic core as shown in FIG. 22 are determined based on the magneticcore as a reference because the end portions of the magnetic corethemselves are the magnetic pole surfaces. If the example of FIG. 22 isused for explanation and the vertical direction in the drawing isassumed to be the imaginary axis direction, the positions indicated bythe arrows I and J are the “end portions in the imaginary axisdirection”.

According to the present invention, of the two electrodes, at least apart of the one electrode (electrode 12 in this embodiment mode) islocated in the area F, and the forwardmost end portion of the otherelectrode (electrode 11 in this embodiment mode) is located in the areaoutside the area F.

FIGS. 23 to 26 show examples of forms of the electrode arrangementapplicable to the present invention. The form of FIG. 23 represents theform of this embodiment mode, and the others correspond to modifiedexamples of this embodiment mode. In FIGS. 1 and 23, the forwardmost endportion of the electrode 12 is located in the area F, and theforwardmost end portion of the electrode 11 is located outside the areaF so as to be opposed to the electrode 12.

To the contrary, the forms in which the electrodes are slided in theimaginary axis (axis of the electrode 12) direction correspond to themodified examples of FIGS. 24 to 26.

In FIG. 24, the forwardmost end portion of an electrode 12 a is locatedin the area F, and an electrode 11 a is located so as to be opposed tothe electrode 12 a in the state where the imaginary plane X defining thearea F coincides with the forwardmost end portion of the electrode 11 a.Thus, according to the present invention, the state where the electrode11 a corresponding to “the other electrode” contacts the area F is alsoincluded in the case of “being located in the area outside the areasurrounded by the two imaginary planes and the magnetic pole surfaces”.In other words, the expression “outside the area” represents the conceptincluding a boundary line of the area.

In FIG. 25, the imaginary plane X and the forwardmost end portion of anelectrode 12 b are located so as to coincide with each other, and theforward most end portion of an electrode 11 b is located outside thearea F so as to be opposed to the electrode 12 b. Further, in FIG. 26,an electrode 12 c penetrates the area F with its forwardmost end portionlocated outside the area F, and the forwardmost end portion of anelectrode 11 c is naturally located outside the area F so as to beopposed to the electrode 12 c. Thus, according to the present invention,even if the forwardmost end portions of the electrodes 12 b and 12 ceach corresponding to “the one electrode” are located outside the areaF, there is no problem as long as at least a part of each of theelectrodes is included in the area F.

It is assumed that by arranging the two electrodes as described above,the magnetic flux density of the magnetic field having the vectorcomponent appropriate for confining the discharge plasma in a magneticfield is greatly increased, thereby further increasing the purity of acarbon nanotube to be manufactured. Also, if the “electrode at least apart of which is located in the area F” corresponding to “the oneelectrode” is arranged to be the electrode 12 as in this embodimentmode, the carbon nanotubes grow and are deposited on the end portion ofthe electrode 11 corresponding to “the other electrode”, so that themanufactured carbon nanotubes are located in the position outside thearea surrounded by the magnetic pole surfaces of the permanent magnets20 to 23. Therefore, in collecting the manufactured carbon nanotubes orreplacing the electrodes 11, it is unnecessary to take out the electrode11 from the area surrounded by the magnetic pole surfaces of thepermanent magnets 20 to 23. That is, without moving the electrode 11,the manufactured carbon nanotubes can be collected (for example, byscraping off using a spatula or drawing using a suction apparatus), andby sliding the electrode 11 in a direction perpendicular to the takeoutoperation (in the vertical direction of FIG. 1), the electrodes 11 canbe replaced. Accordingly, if the carbon nanotubes are located in theposition outside the area surrounded by the magnetic pole surfaces ofthe permanent magnets 20 to 23, it becomes easy to handle the carbonnanotubes, thereby realizing the increase in high productivity for thecarbon nanotubes.

The range of length of gaps between both the forward end portions of theelectrodes 11 (a to c) and the forward end portions of the electrodes12(a to c), respectively, is selected from the range enough to generatethe discharge plasma, and determined by itself based on the voltagedrop. Generally, the range is selected from the range approximatelybetween 0.1 to 5 mm.

Also, there is a condition that the generation areas of the dischargeplasma between the electrodes 11 (a to c) and the electrodes 12 (a toc), respectively, are in the position on which the magnetic field due tothe permanent magnets 20 to 23 effects, so that the distance between theelectrodes 12 (a to c) and the imaginary plane Y is also determined byitself based on the magnetic force and the like of the permanent magnets20 to 23. Specifically, it is preferable to set the distance within sucha range as to satisfy “the magnetic flux density in the discharge area”described later.

Next, a description will be made of examples of manufacturing a carbonnanotube by using the manufacturing apparatus for a carbon nanotube ofthis embodiment mode.

A reaction container (chamber) 10 is a sealed container in a cylindricalshape (disposed such that both the bottom surfaces face upward anddownward respectively in the drawing), and the container is desirablymade of metal, especially stainless steel, and may be suitably made ofan aluminum alloy, quartz, and the like. Additionally, the shape is notlimited to the cylindrical shape, and a desired shape such as a boxshape may be used. Further, in the case where the atmosphere of thedischarge area is an atmosphere of air at an atmospheric pressure andthe carbon nanotubes are to be adhered around the forwardmost endportion of the electrode 11, the reaction container 10 is notindispensable, or the reaction container 10 is not necessarily a sealedcontainer.

The two electrodes 11 and 12 whose forwardmost end portions are opposedto each other are disposed in the reaction container 10. At this time,when the material of the reaction container 10 is the one havingelectric conductivity such as metal, the reaction container 10 and theelectrode 11 and electrode 12 are fixed while they are electricallyinsulated from each other. Note that as the arrangement of the twoelectrodes 11 and 12, in addition to the state as shown in FIG. 1 inwhich both the axes coincide with each other so as to be opposed to eachother completely, the state may be possible in which the axes of the twoelectrodes 11 and 12 have a certain angle and the forwardmost endportions are made close to each other. In the present invention, theexpression “the forwardmost end portions are opposed to each other”,represents the concept including the latter case described above.Naturally, the former form as shown in FIG. 1 is desirable.

As to the arrangement of the electrodes 11 and 12, when the opposingsurfaces of the electrode 11 and the electrode 12 are arranged inparallel, the stable discharge such as arc discharge can be realized,and the carbon nanotubes can be synthesized efficiently.

Carbon is desirable as the material of the two electrodes 11 and 12, buta substance that contains carbon and has an electric resistivity of 0.01Ω·cm or more and 10 Ω·cm or less (preferably 0.01 Ω·cm or more and 1Ω·cm or less) is suitably used.

The shape of the two electrodes 11 and 12 are not limited, and examplesof the shape may include a cylindrical shape, a rectangular columnshape, and a truncated cone shape, but the cylindrical shape isdesirable. In addition, the diameter of the forwardmost end portion (inthe case where the forward most end portion is not circular, thediameter of a circle having the same area as the forwardmost endportion) of the two electrodes 11 and 12 is not especially limited, butpreferably 1 mm or more and 100 mm or less.

As to the opposing two electrodes 11 and 12, the area of the forwardmostend portion of the electrode 11 serving as the cathode is desirablyequal to or less than the area of the forwardmost end portion of theelectrode 12 serving as the anode. The purity of the obtained carbonnanotube is further increased when the area of the forwardmost endportion of the cathode is equal to or less than the area of theforwardmost end portion of the anode. The ratio of the areas betweenthem (the area of the forwardmost end portion of the cathode/the area ofthe forwardmost end portion of the anode) is preferably 0.1 to 0.9, andmore preferably 0.2 to 0.5.

In order to stabilize the discharge, it is preferable that theelectrodes 11 and 12 are cooled with water to thereby suppress theincrease in temperature of the electrodes. If the electrodes 11 and 12are to be cooled with water, it is desirable to use the metal high inheat conductivity, in particular copper, for supporting portions for theelectrodes 11 and 12.

By using atmosphere adjusting means including a vacuum pump 14, a gascylinder 17, an inlet tube 15, and a valve 19 to appropriately adjustthe atmosphere inside the reaction container 10, the atmosphere in thedischarge area is set to a desired state. Specifically, the vacuum pump14 can decompress or compress the inside of the reaction container 10.After the inside of the reaction container 10 is decompressed by thevacuum pump 14, the valve 19 is opened, and a desired gas stored in thegas cylinder 17 is introduced into the reaction container 10 through theinlet tube 15, thereby making it possible to obtain the desired gasatmosphere. Naturally, the operation for adjusting the atmosphere isunnecessary when the atmosphere is the atmosphere of air at theatmospheric pressure.

Examples of the vacuum pump 14 include a rotary pump, a diffusion pump,and a turbo molecule pump.

The pressure of the atmosphere inside the reaction container 10 (thatis, atmosphere in the discharge area, used in the same sensehereinafter) may be 0.01 Pa or more and 510 kPa or less, preferably 0.1Pa or more and 105 kPa or less, and more preferably 13 Pa or more and 70kPa or less. Under such a pressure, high purity carbon nanotubes can bemanufactured.

The atmospheric gas in the reaction container 10 is not specificallylimited, and air, helium, argon, xenon, neon, nitrogen, hydrogen, andmixture of those gases are desirable. In the case of introducing adesired gas, after the inside of the reaction container 10 is exhaustedby the vacuum pump 14, the desired gas is introduced up to apredetermined pressure from the gas cylinder 17.

According to the present invention, the atmosphere inside the reactioncontainer 10 can further store a gas including a substance containingcarbon. In this case, the atmosphere may only include the gas includingthe substance containing carbon, or the gas including the substancecontaining carbon may be introduced into the atmosphere of the differenttypes of gases described above. By adding the gas including thesubstance containing carbon to the atmosphere, it is possible tomanufacture a carbon nanotube having an anomalous structure. This carbonnanotube has a structure of carbon grown around a carbon nanotube as acenter axis.

The applicable substance containing carbon is not limited, andhydrocarbons such as ethane, methane, propane, and hexane; alcohols suchas ethanol, methanol, and propanol; ketones such as acetone; petroleums;gasolines; inorganic substances such as carbon monoxide, and carbondioxide; or the like, can be used. Acetone, ethanol, and hexane areespecially preferable.

In the manufacturing apparatus for a carbon nanotube according to thisembodiment mode on which the conditions described above are set, byapplying the voltage from the power supply 18 between the electrodes 11and 12, discharge plasma is generated between the electrodes 11 and 12.The types of the discharge plasma include arc plasma and glow plasma.Arc plasma is preferable for efficiently manufacturing the carbonnanotube.

When the arc discharge is generated, contact arc process may beconducted before the arc discharge generation. The contact arc processis a process in which after the voltage is applied while the electrodes11 and 12 are in contact with each other, the moving apparatus 13separates the electrodes 11 and 12 to a certain inter-electrodedistance, and discharge plasma is generated. Through this process,stable discharge plasma is generated easily and quickly.

The voltage applied between the electrodes 11 and 12 may be a DC or anAC, but the DC is preferable for increasing the purity of the carbonnanotube to be obtained. Note that in the case of applying the AC, thereis no distinction between the electrodes 11 and 12 in terms of polarity.

The current density of the discharge when the discharge plasma isgenerated is preferably 0.05 A/mm² or more and 15 A/mm² or less, andmore preferably 1 A/mm² or more and 5 A/mm² or less with respect to thearea of the forwardmost end portion of the electrode generating thedischarge plasma. “The electrode generating the discharge plasma”indicates the cathode when the applied voltage is the DC, and indicatesthe electrode with the smaller forwardmost end portion area when theapplied voltage is the AC (this holds true throughout the description inthe present invention).

The voltage applied between the electrodes 11 and 12 by the power supply18 is preferably 1 V or more and 30 V or less, and more preferably 15 Vor more and 25 V or less. As a result of the discharge, the forward endportion of the electrode 12 is being consumed, so that the intervalbetween the electrodes 11 and 12 changes during the discharge. It ispreferable to control the voltage between the electrodes 11 and 12 tobecome constant by appropriately adjusting the interval between theelectrodes 11 and 12 using the moving apparatus 13.

The period for applying the voltage is preferably set to 3 seconds ormore and 180 seconds or less, and more preferably 5 seconds or more and60 seconds or less. When the period is less than 3 seconds, the appliedvoltage is unstable, so that the purity of the carbon nanotube to beobtained may be reduced. When the period exceeds 180 seconds, theradiant heat due to the discharge plasma may reduce the magnetic fluxdensity of the permanent magnets 20 to 23, or as a result of exceeding aCurie temperature, the magnetic field intensity may be lost. Thus, boththe cases are not preferable.

In order to eliminate the defect due to the increase in temperature ofthe permanent magnets 20 to 23, the form is also preferable in whichcooling means is provided for the permanent magnets 20 to 23. Byproviding the cooling means, the period for applying the voltage can beset to be longer. Examples of the cooling means include means formed byattaching a heat releasing member to the permanent magnets 20 to 23 andmeans for cooling the permanent magnets 20 to 23 with water.

FIGS. 27-a and 27-b are schematic views showing an example of thecooling means formed by attaching the heat releasing member to each ofthe permanent magnets 20 to 23, which is typified by the permanentmagnet 20. FIG. 27-a is a side view around the permanent magnet attachedwith the heat releasing member, and FIG. 27-b is a front view observedfrom the right (the side of a surface to be opposed to theabove-mentioned imaginary axis) of FIG. 27-a. In FIGS. 27-a and 27-b,the permanent magnet 20 indicated by dotted lines is embedded into ablock-shaped copper lump 32 and covered with a copper lid 34, so as tobe completely surrounded by a heat releasing member 30 composed of thecopper lump 32 and the copper lid 34.

The heat of the permanent magnet 20 is released by the heat releasingmember 30, so that the heat accumulation is suppressed. Note that as thematerial of the heat releasing member 30, copper is used in thisexample, but there is no limitation thereto. Any material high in heatconductivity can be adopted, and it is preferable to use a metal, inparticular copper.

FIGS. 28-a and 28-b are schematic views showing an example of thecooling means formed by attaching the heat releasing member to each ofthe permanent magnets 20 to 23 and further subjecting this to watercooling. FIG. 28-a is a cross sectional view of the permanent magnetsand a periphery of the electrode taken along a direction of sidesurfaces thereof, and FIG. 28-b is a cross sectional view taken along aline B-B of FIG. 28-a. In FIGS. 28-a and 28-b, the permanent magnets 20to 23 indicated by dotted lines is in the same form as the state shownin FIGS. 27-a and 27-b, that is, completely surrounded by the heatreleasing member 30. In addition, a tube 36 across the insides of thefour heat releasing members 30 and a tube 38 surrounding the outsides ofthe four heat releasing members 30 are respectively installed, and watercirculates through these tubes.

The heat of the permanent magnets 20 to 23 are released by the heatreleasing members 30, and the heat releasing members 30 are furthercooled with water circulating inside the tubes 36 and 38, so thateffectively suppress the heating of the permanent magnets 20 to 23 iseffectively suppressed. Note that a coolant circulating through thetubes 36 and 38 is not limited to water, and any conventionally knowncoolant, whether it is liquid or gas, can be used. Further, as thematerials of the tubes 36 and 38, similarly to the heat releasingmembers 30, any material high in heat conductivity is preferable, and itis preferable to use a metal, in particular copper.

Incidentally, when discussing “the end portions in the imaginary axisdirection” of the magnet to be discussed when each of the permanentmagnets 20 to 23 is completely surrounded by the heat releasing member30 are naturally determined by the position of each of the embeddedpermanent magnets 20 to 23, and are not affected by the positions of theheat releasing member 30 and tubes 36 and 38. Therefore, as shown inFIG. 28-a, the imaginary plane formed by connecting end portions on oneside in the imaginary axis direction and the imaginary plane formed byconnecting end portions on the other side are in the positions indicatedby X′ and Y′.

The magnetic flux density in the discharge area is preferably 10⁻⁵ T ormore and 1 T or less in the forwardmost end portion of the electrodegenerating discharge plasma of the two opposing electrodes 11 and 12.When the magnetic flux density is less than 10⁻⁵ T, it is difficult toform an effective magnetic field, and when the magnetic flux densityexceeds 1 T, it may be difficult to dispose the permanent magnets 20 to23, which generate the magnetic field inside the apparatus, close to thegeneration area of the discharge plasma. Thus, both the cases are notpreferable. When the magnetic flux density is 10⁻⁴ T or more and 10⁻² Tor less, the stable discharge is generated, thereby making it possibleto efficiently produce a carbon nanotube.

When the discharge plasma is generated between the electrodes 11 and 12as described above, carbon is separated from the surface of theelectrode 11, and then reacts to produce carbon nanotubes. The producedcarbon nanotubes are deposited mainly on the surface of the forwardmostend portion of the electrode 11 or in a periphery thereof.

As has been described above, according to this embodiment mode, it ispossible to manufacture an extremely high density carbon nanotube withease at low costs while using the discharge plasma method such as arcdischarge. In particular, depending on the conditions, the purity of thecarbon nanotube can be 95% or more.

Embodiment Mode 2

Next, a description will be given of a manufacturing apparatus for acarbon nanotube according to Embodiment Mode 2 of the present invention,which achieves a mass-productivity of the carbon nanotubes at a higherlevel. FIG. 29 is a schematic cross sectional view showing themanufacturing apparatus for a carbon nanotube according to EmbodimentMode 2 of the present invention. The manufacturing apparatus of thisembodiment mode has the same structure as the manufacturing apparatusaccording to Embodiment Mode 1, but differs therefrom in terms ofarrangement of the cathodes and holding method therefor. Both theapparatuses basically are the same except for the above. Thus, in FIG.29, members having the same function as those in Embodiment Mode 1 aredenoted by the same reference numerals as in FIG. 1 and a detaileddescription thereof will be omitted here.

In this embodiment mode, any one selected from the rod-shaped electrodegroup 41 arranged on a disc-like holding member 42 in a bristling mannerconstitutes a cathode corresponding to “the other electrode” in thepresent invention. FIG. 30 is a cross sectional view (cross sectionalview only showing permanent magnets, electrodes, and the holding member)taken along the line C-C of FIG. 29. As shown in FIG. 29, the rod-shapedelectrode group 41 has 12 rod-shaped electrodes 41 a to 41 m arranged ina bristling manner on the holding member 42 concentrically with theholding member. Each of the rod-shaped electrodes 41 a to 41 m iselectrically connected with the power supply 18 through the holdingmember 42. Also, the holding member 42 is arranged rotatably in thedirection of the arrow D.

In the state shown in FIG. 30, the rod-shaped electrode 41 a (indicatedby the dotted line in FIG. 30) positioned just below the electrode 12and opposed thereto serves as the cathode corresponding to “the otherelectrode” in the present invention. However, through the rotation ofthe holding member 42 in the direction of the arrow D, the otherrod-shaped electrodes 41 b to 41 m can be each positioned just below theelectrode 12 and opposed thereto, and thus can serve as the cathodecorresponding to “the other electrode” in the present invention. At thistime, the rod-shaped electrodes 41 a to 41 m each serving as “the otherelectrode” in the present invention are located in the area outside thearea F, that is, below the permanent magnets 20 to 23. Therefore, nomatter how the holding member 42 rotates, there is no obstacle to itsrotation. As a result, the holding member can freely rotate.

Assuming here that the voltage is applied between the electrode 12 andthe rod-shaped electrode 41 a from the power supply 18 to therebygenerate the discharge plasma between both the electrodes, the carbonnanotubes are produced and deposited at the forwardmost end portion ofthe rod-shaped electrode 41 a and its vicinity. After the completion ofthe voltage application, the holding member 42 is rotated in thedirection of the arrow D, so that the rod-shaped electrode 41 b ispositioned just below the electrode 12 this time. In this state, thevoltage is applied between the electrode 12 and the rod-shaped electrode41 b from the power supply 18. In this way, the carbon nanotubes growand are deposited at the forwardmost end portion of the rod-shapedelectrode 41 b and its vicinity. This operation is repeatedly performedon the rod-shaped electrodes 41 c to 41 m as well. Thus, the carbonnanotubes grow and are deposited at the forward most end portion of eachof the 12 rod-shaped electrodes 41 a to 41 m and its vicinity insuccession. In other words, according to the manufacturing apparatus forthe carbon nanotube of this embodiment mode, high productivity can beachieved while maintaining extremely high purity of the produced carbonnanotube.

The rod-shaped electrodes 41 a to 41 m where the carbon nanotubes aredeposited can be each replaced as they are on the basis of the holdingmember 23. Alternatively, while rotating the holding member 23, theelectrodes located at the positions of the rod-shaped electrodes 41 d to41 j in the figure are first removed and new ones may be reset. Thecarbon nanotubes deposited in the forwardmost end portion of each of thecollected rod-shaped electrodes 41 a to 41 m and its vicinity arecollected by scraping off or drawing the carbon nanotubes asappropriate. This enables the efficient mass production of the carbonnanotubes with high purity.

Also, instead of collecting the rod-shaped electrodes 41 a to 41 m,while rotating the holding member 23 as it is, the carbon nanotubesdeposited in the forwardmost end portion of each of the electrodeslocated at the positions of the rod-shaped electrodes 41 d to 41 j inthe figure can be first collected as well by scraping off or drawing thecarbon nanotubes as appropriate. In this case, each of the rod-shapedelectrodes 41 a to 41 m after the carbon nanotubes are collected can beused again for the generation of the discharge plasma.

Note that in this embodiment mode, the form in which the number ofrod-shaped electrodes is 12 has been described. However, no particularlimitation is imposed on the number thereof, and as many electrodes asdesired can be used from the viewpoint of efficient mass production ofthe carbon nanotubes. Even if only one rod-shaped electrode is arrangedon the holding member 42, the electrode is moved to a large space wherethe permanent magnets 20 to 23 are not positioned above the electrodebefore the various operations such as the electrode replacement or thecollection of the carbon nanotubes can be made. Thus, the highoperability can be obtained.

Also, in this embodiment mode, the case in which the disc-like holdingmember 42 is used has been described by way of example. However, noparticular limitation is imposed on the shape of the holding member. Theholding member may take, for example, a long-plate shape, on which therod-shaped electrodes are linearly bristled. Alternatively, the holdingmember may take a rectangular shape, on which the rod-shaped electrodesare bristled two-dimensionally, for example, in parallel, in a zigzagform, or at random. The holding member may take another shape or aflexible belt-like shape.

Embodiment Mode 3

Next, a description will be given of a manufacturing apparatus for acarbon nanotube according to Embodiment Mode 3 of the present invention,which includes collecting means having a mechanism for scraping thecarbon nanotubes and achieves mass-productivity of the carbon nanotubesat a higher level. FIG. 31 is a schematic cross sectional view showingthe manufacturing apparatus for a carbon nanotube according toEmbodiment Mode 3 of the present invention. The manufacturing apparatusof this embodiment mode has the same structure as the manufacturingapparatus according to Embodiment Mode 1, but differs therefrom in termsof arrangement of the cathodes and provision of the collecting means.Both the apparatuses basically are the same except for the above. Thus,in FIG. 31, members having the same function as that in Embodiment Mode1 are denoted by the same reference numeral as in FIG. 1, and a detaileddescription thereof will be omitted here.

As shown in FIG. 31, a drum-like rotary member 51 is arranged with itsperipheral surface opposite to the electrode 12. In this embodimentmode, the rotary member 51 constitutes the cathode corresponding to “theother electrode” in the present invention. As mentioned above, theelectrode having the shape other than the rod shape can be used as theelectrode in the present invention as far as the electrode contributesto the generation of the discharge plasma. In this case, the portion ofthe peripheral surface of the rotary member 51 opposite to the electrode12 corresponds to “the forwardmost end portion” specified in the presentinvention.

The rotary member 51 is pivotally supported by a support 53 about anaxis 52 while freely rotating in the direction of the arrow E by anunillustrated rotating apparatus. At this time, the rotary member 51corresponding to “the other electrode” in the present invention islocated in the area outside the area F, that is, below the permanentmagnets 20 to 23. Therefore, there is no obstacle to its rotation, sothat the rotary member 51 can freely rotate.

Note that the rotary member 51 is electrically connected with the powersupply 18 through the support 53 and the axis 52.

FIG. 32 is an enlarged perspective view of only the rotary membercorresponding to the cathode in this embodiment mode and the collectingmeans in the vicinity thereof in an extracted fashion. As shown in FIG.31 and FIG. 32, on the downstream side of a site of the rotary member 51opposite to the electrode 12 in the rotating direction thereof(direction of the arrow E), a blade 54 is disposed and abutted againstthe peripheral surface of the rotary member 51 at an acute angle. Also,a carbon nanotube container 55 is disposed below the abutment portion.

Assuming here that the voltage is applied between the electrode 12 andthe rotary member 51 from the power supply 18 to thereby generate thedischarge plasma between both the electrodes, the carbon nanotubes areproduced and deposited on the peripheral surface of the rotary member51. After the completion of the voltage application, the rotary member51 is rotated in the direction of the arrow E up to the position atwhich the portion where the carbon nanotubes are deposited is abuttedagainst the blade 54. At this position, the carbon nanotubes are scrapedoff by the blade 54. The scraped carbon nanotubes fall by gravitation tobe received in the carbon nanotube container 55.

Also, after the completion of the voltage application, the carbonnanotubes are produced/deposited at a predetermined portion on theperipheral surface of the rotary member 51. After that, the rotarymember 51 is slightly rotated to set another portion on the peripheralsurface of the rotary member so as to oppose the electrode 12. Then, thepower supply 18 applies the voltage between the electrode 12 and therotary member 51, so that the carton nanotubes grow and are deposited atthe newly set portion on the peripheral surface of the rotary member 51as well. This operation is repeatedly performed to thereby have thecarbon nanotubes produced/deposited on the peripheral surface of therotary member 51 successively. Thus, the portion where the carbonnanotubes are deposited ahead of the other portions reaches the positionwhere the blade 54 is abutted against the rotary member. Thus, thecarbon nanotubes thereon are automatically scraped off by the action ofthe blade 54. In other words, according to the manufacturing apparatusfor the carbon nanotube of this embodiment mode, the carbon nanotubescan be mass-produced successively with high productivity whilemaintaining extremely high purity of the produced carbon nanotube.

Note that, in this embodiment mode, the form in which the blade and thecontainer are used in combination as the collecting means has beendescribed by way of example. However, the collecting means in thepresent invention is not limited to this. For example, as the member forscraping the deposited carbon nanotubes, a brush, sponge, etc. can beused instead of using the blade. As another structure, an adhesive maybe used to adhere the carbon nanotubes thereto.

Also regarding the form of the electrode, in this embodiment mode, “theother electrode” has the drum-like shape for convenience of apparatusstructure. However, the electrode is not limited to this but may takethe rod shape as in the general cases and a polyhedral shape like a cubeetc., and in addition, a belt-like shape.

Given as a modification of the collecting means is a mechanism fordrawing the deposited carbon nanotubes, which is provided withoutchanging the form of Embodiment Mode 1 or is applicable to any otherforms. For example, there can be given a mechanism in which a suctionapparatus utilizing the reduced pressure is prepared, pipes for suctionare provided, and openings (suction openings) at end portions thereofare caused to approach the forwardmost end portion of the electrodewhere the carbon nanotubes are deposited to directly take in the carbonnanotubes. The suction opening is not always needed to approach theforwardmost end portion of the electrode, but the suction opening may beformed so as to approach the electrode after the carbon nanotubes aredeposited (needless to say, even if the suction opening approaches theforwardmost end portion of the electrode all the time, there arises noproblem provided that an ON/OFF control is made on the operation of thesuction apparatus).

In any case, according to the manufacturing apparatus for the carbonnanotube of the present invention, the cathode where thegrowth/deposition of the carbon nanotubes takes place is surrounded bythe magnetic pole surfaces of the plural magnets or positioned outsidethe surrounded area. Thus, various collecting means can be easily set.As a result, by providing the various collecting means, extremely highproductivity can be ensured while maintaining the high purity of thecarbon nanotube.

MORE SPECIFIC EXAMPLE

Hereinafter, the present invention will be specifically described basedon an example. However, the present invention is not limited to theexample.

In this example, the carbon nanotubes are manufactured mainly using themanufacturing apparatus for the carbon nanotube shown in FIG. 1. Notethat the manufacturing apparatus equipped with the cooling means withthe structure shown in FIG. 28-a and FIG. 28-b is used.

Specific conditions for the respective structures are as follows.

-   -   Reaction container 10: A cylindrical container chamber made of        stainless steel with a diameter of 210 mm and a length of 380        mm.    -   Electrode (cathode) 11: A cylindrical graphite rod with an outer        diameter of 5 mm (purity: 99.9% or more).    -   Electrode (anode) 12: A cylindrical graphite rod with an outer        diameter of 15 mm (purity: 99.9% or more).    -   Forwardmost end portion position of the electrode 11: A distance        from the midpoint between the imaginary plane X and the        imaginary plane Y (hereinafter, abbreviated to h in some cases)        is set to the following 4 levels:

-   (1) h=0 mm (midpoint between the imaginary plane X and the imaginary    plane Y: within the area F)

-   (2) h=3 mm below the midpoint (8 mm above the imaginary plane Y:    within the area F)

-   (3) h=9 mm below the midpoint (2 mm above the imaginary plane Y:    within the area F)

-   (4) h=15 mm below the midpoint (4 mm below the imaginary plane Y:    outside the area F)    -   Moving apparatus 13: An apparatus makes the electrode 11 movable        with a stepping motor, with such an adjustment as to keep a        distance between the electrodes 11 and 12 constant during the        plasma discharge.    -   Power supply 18: ADC arc welding power supply (AR-SB300        manufactured by OSAKA DENKI KIKOU Co., LTD.) capable of        controlling the current value from 20 A to 300 A.    -   Permanent magnets 20 to 23: Cylindrical NdFB permanent magnets        with a diameter of 22 mm and a thickness of 10 mm (diameter: 22        mm, thickness: 10 mm, manufactured by Niroku Seisakusho). The        permanent magnets 20 to 23 are incorporated as the cooling means        as shown in FIG. 28-a and FIG. 28-b. At this time, in more        detail, as shown in FIG. 27-a and FIG. 27-b, the permanent        magnets 20 to 23 are embedded into the heat releasing member 30        made of copper (length: 50 mm, width: 40 mm, thickness: 25 mm,        and thickness of the copper cover 34: 2.5 mm). The copper-made        tubes 36 and 38 are further routed, the coolant is circulated        through the tubes 36 and 38, and the temperature is controlled        so as to maintain the temperature of the permanent magnets 20 to        23 below 100° C. during the discharge. As a result, the        temperature of the permanent magnets 20 to 23 does not exceed        Curie point during the discharge. The minimum distance between        the opposing permanent magnets is 82 mm. The magnetic flux        density at the edge of the forwardmost end portion of the        electrode 11 is 7 mT.

The manufacturing apparatus described above was used to manufacture thecarbon nanotubes. The inside of the reaction container 10 was notdecompressed, and the operation was conducted in the atmosphere at101.325 kPa (1 atmospheric pressure). To generate arc discharge betweenthe electrodes 11 and 12, the contact arc process was conducted first,and then, the electrodes 11 and 12 were separated by about 1 mm to 3 mmafter the start of the discharge. The voltage applied by the powersupply 18 was a DC voltage of 25 V to 30 V. The distance between theelectrodes was adjusted so as to keep the voltage constant. The arcdischarge was conducted under the above conditions for about 1 minute.The current value was 80 A, and the discharge current density withrespect to the forwardmost end portion area of the electrode 11 was 4.1A/mm².

After the discharge, the electrode 11 was taken out, and the forwardmostend portion was observed using a scanning electron microscope. For theobservation using the scanning electron microscope, a scanning electronmicroscope S-4500 manufactured by Hitachi Ltd., was used. Through theobservation using the scanning electron microscope, it has beenconfirmed that the high-purity carbon nanotube is produced irrespectiveof the position of the forwardmost end portion of the electrode 11. Asthe distance h from the midpoint between the imaginary plane X and theimaginary plane Y becomes large, the purity is more increased. It hasbeen confirmed that in the case of the distance of 9 mm or more, almostno purity is observed. Also, when h=15 mm, no purity is observed throughthe observation on the photograph.

Through the image processing on the scanning electron microscope image,the purity of the carbon nanotube is estimated. FIG. 33 is a graphshowing a transition of the purity according to the position of theforwardmost end portion of the electrode 11 (distance h from themidpoint between the imaginary plane X and the imaginary plane Y). Inthe case where (4) the distance is 15 mm below the midpoint between theimaginary plane X and the imaginary plane Y, the purity is 95% or more.

Also, regarding the position of the forwardmost end portion of theelectrode 11, when (3) h=9 mm as the distance from the midpoint betweenthe imaginary plane X and the imaginary plane Y and (4) h=15 mm,scanning electron microscope photographs of the forwardmost end portionof the electrode 11 in the respective cases are shown in FIG. 34 andFIG. 35.

As described above, the condition of the magnetic field is optimized, sothat the carbon nanotubes with the extremely high purity can be directlysynthesized without using any catalyst or involving any purificationprocess.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to efficientlysynthesize the high-purity carbon nanotubes such as amorphous carbonparticles and the graphite particles with extremely low impurityconcentration on an industrial scale. In particular, according to thepresent invention, the mass-production of the high-purity carbonnanotubes can be achieved on the industrial scale based on the formthereof.

1. A manufacturing apparatus for a carbon nanotube, comprising: at leasttwo electrodes whose forwardmost end portions are opposed to each other;a power supply for applying a voltage between the electrodes in order togenerate discharge plasma in a discharge area between the electrodes;and plural magnets configured to form a magnetic field in a generationarea of the discharge plasma by generating a magnetic field from amagnetic pole surface of each of the plural magnets, characterized inthat: the plural magnets are arranged to have the magnetic pole surfacesthereof opposed to one imaginary axis within a space; and of the twoelectrodes, at least a part of one electrode is located in an areasurrounded by: an imaginary plane formed by connecting end portions ofthe magnetic pole surfaces of the plural magnets on one side in adirection of the imaginary axis; an imaginary plane formed by connectingend portions thereof on the other side; and the magnetic pole surfacesof the plural magnets, and the forwardmost end portion of the otherelectrode is located in an area outside the area surrounded by the twoimaginary planes and the magnetic pole surfaces.
 2. A manufacturingapparatus for a carbon nanotube of claim 1, characterized in that theone electrode is an anode.
 3. A manufacturing apparatus for a carbonnanotube of claim 2, characterized in that plural rod-shaped electrodesare placed in parallel in a bristling manner, and any one of therod-shaped electrodes has a forwardmost end portion opposed to theforwardmost end portion of the one electrode and can be moved to aposition so as to serve as the other electrode.
 4. A manufacturingapparatus for a carbon nanotube nanotube of claim 2, characterized bycomprising collecting means for collecting carbon nanotubes that aremanufactured by generating discharge plasma between the two electrodesand remain adhering to the forwardmost end portion of the otherelectrode.
 5. A manufacturing apparatus for a carbon nanotube of claim4, characterized in that the collecting means has a mechanism forscraping off the carbon nanotubes adhering to the forwardmost endportion of the other electrode.
 6. A manufacturing apparatus for acarbon nanotube of claim 4, characterized in that the collecting meanshas a mechanism for drawing the carbon nanotubes adhering to theforwardmost end portion of the other electrode.
 7. A manufacturingapparatus for a carbon nanotube of claim 1, characterized in that thedischarge plasma generated in the discharge area is arc plasma.
 8. Amanufacturing apparatus for a carbon nanotube of claim 1, characterizedin that the plural magnets are arranged to surround the one electrodesuch that all the magnetic pole surfaces of the same poles are opposedto the imaginary axis.
 9. A manufacturing apparatus for a carbonnanotube of claim 1, characterized in that the even number of magnets,equal to or greater than four, are arranged to surround the oneelectrode such that each magnetic pole surface opposed to the imaginaryaxis has a pole alternately opposite to that of the adjacent magneticpole surface.
 10. A manufacturing apparatus for a carbon nanotube ofclaim 1, characterized in that, of the two electrodes, the electrodethat generates the discharge plasma has a magnetic flux density of 10⁻⁵T or more and 1 T or less at an edge of the forwardmost end portionthereof.
 11. A manufacturing apparatus for a carbon nanotube of claim 1,characterized in that a density of a discharge current at a time ofgenerating the discharge plasma is 0.05 A/mm² or more and 15 A/mm² orless with respect to an area of the forwardmost end portion of theelectrode that generates the discharge plasma.
 12. A manufacturingapparatus for a carbon nanotube of claim 1, characterized in that thevoltage applied to the electrodes by the power supply is 1 V or more and30 V or less.
 13. A manufacturing apparatus for a carbon nanotube ofclaim 1, characterized in that an area of the forwardmost end portion ofa cathode of the two electrodes is equal to or less than the area of theforwardmost end portion of the anode thereof.
 14. A manufacturingapparatus for a carbon nanotube of claim 1, characterized in that atleast the discharge area and the two electrodes are received in a sealedcontainer.
 15. A manufacturing apparatus for a carbon nanotube of claim1, characterized in that at least the discharge area and the twoelectrodes are received in the sealed container, and atmosphereadjusting means capable of adjusting an atmosphere inside a sealedcontainer is provided.
 16. A manufacturing apparatus for a carbonnanotube of claim 1, characterized in that the material of theelectrodes is carbon or a substance that contains carbon and has anelectric resistivity equal to or more than 0.01 Ω·cm and equal to orless than 10 Ω·cm.
 17. A manufacturing method for a carbon nanotube,characterized in that: the manufacturing apparatus for a carbon nanotubeof claim 1 is used; and by applying a voltage between the two electrodesinside the manufacturing apparatus, discharge plasma is generated in adischarge area between the electrodes to thereby manufacture the carbonnanotube.
 18. A manufacturing method for a carbon nanotube of claim 17,characterized in that a voltage applied between the two electrodes is aDC voltage such that the one electrode of the manufacturing apparatusfor a carbon nanotube as described in (1) is an anode.
 19. Amanufacturing method for a carbon nanotube of claim 17, characterized inthat the discharge plasma generated in the discharge area is arc plasma.20. A manufacturing method for a carbon nanotube of claim 17,characterized in that a pressure of an atmosphere of the discharge areais 0.01 Pa or more and 510 kPa or less.
 21. A manufacturing method for acarbon nanotube of claim 17, characterized in that an atmosphere of thedischarge area is a gas atmosphere that contains at least one of gasesselected from air, helium, argon, xenon, neon, nitrogen, and hydrogen.22. A manufacturing method for a carbon nanotube characterized in thatan atmosphere of the discharge area further includes a gas that iscomposed of a substance containing carbon.